1. Field
Exemplary embodiments of the present invention relate to a resistance variable memory device and a fabrication method thereof, and more particularly, to a resistance variable memory device using nano particles and a method for fabricating the resistance variable memory device.
2. Description of the Related Art
A resistance variable memory device stores data by using a resistance variable material that may switch between two or more different resistance states because the resistance variable material has its resistance that varies according to an external stimulus. Examples of the resistance variable material include a perovskite-based material and a transition metal oxide. FIG. 1 is a cross-sectional view illustrating a basic structure of a conventional resistance variable memory device and the features of the conventional technology.
Referring to FIG. 1, the resistance variable memory device has a structure where a resistance variable layer 20 is interposed between a lower electrode 10 and an upper electrode 30. Filament-type current paths 40 are formed or disappear in the resistance variable layer 20 according to a voltage applied between the lower electrode 10 and the upper electrode 30. When the current paths 40 are formed, the resistance variable layer 20 has a low resistance. When the current paths 40 disappear, the resistance variable layer 20 has a high resistance. A set operation is when the resistance variable layer switches from a high resistance state to a low resistance state, and conversely, a reset operation is when the resistance variable layer switches from a low resistance state to a high resistance state.
According to the conventional technology, vacancies, which are a sort of defect, are non-uniformly distributed in the resistance variable layer 20, and the current paths 40 are formed randomly in the resistance variable layer 20. In other words, although the same voltage is applied between the lower electrode 10 and the upper electrode 30, the positions and the number of the current paths 40 may be different. The non-uniform distribution of the current paths 40 makes set voltage/current and reset voltage/current non-uniform as well, which deteriorates the uniformity of switching.
Also, set or reset current depends on the voltage applied between the lower electrode 10 and the upper electrode 30.
However, since the current paths 40 are dispersed into several parts, the current paths 40 may be difficult to control. Particularly, since excessive initial reset current deteriorates device characteristics as switching is performed repeatedly, the reliability of a resistance variable memory device may further deteriorate.
Meanwhile, a method of forming nano dots of a conductive material such as metal in a resistance variable layer that is formed of a transition metal oxide is suggested to address the above features. However, when the resistance variable layer includes conductive nano dots, the voltage applied to the whole memory cell may be difficult to control, and vacancies to be formed in the resistance variable layer may be difficult to form uniformly.